Dung beetle diversity, soil microbes, and soil organic carbon in Coastal California pasturelands

Background/Question/Methods

Soil organic carbon content (SOC) in pasturelands is mediated by the soil microbial community, which is largely affected by influxes of nutrients and the soil arthropod community. One such arthropod, the tunneling dung beetle Onthophagus taurus, incorporates animal dung into the soil, influencing the soil microbial community and nutrient cycling. While dung beetles do affect the soil microbial community, few studies specifically use next generation sequencing to determine if dung beetles change the soil microbial community to favor taxa associated with nutrient cycling and carbon sequestration. Even fewer studies examine dung beetle effects on SOC. In this pilot study we examined how pasture and landscape management influence the diversity and abundance of dung beetles. We also examined how the presence and abundance of tunneling dung beetle O. taurus affects the fungal, bacterial, and archaeal community of pastureland soil in a two month, in situ enclosure experiment in California’s Central Coast region, using eDNA metabarcoding of the 16S and ITS1 loci. We tested three levels of dung beetle abundance (0, 6 and 22 beetles per enclosure).

Results/Conclusions

We found that dung beetle abundance and diversity differed between fields in ranches that differ in grazing management and surrounding landscape conditions. We also found that dung beetle presence and abundance have significant effects on the soil microbial community. A Bray-Curtis PERMANOVA of 16S reads shows that both dung beetle abundance (F=3.973, P=0.001, R2=0.098) and days in experiment (F=4.474, P=0.001, R2=0.165) both affect the soil bacterial archaeal community, with days in experiment having a slightly larger effect. A Bray-Curtis PERMANOVA of ITS1 reads shows that dung beetle abundance (F=6.155, P=0.001, R2=0.147) had a larger effect than days in experiment (F=3.125, P=0.001, R2=0.112). Both dung beetle treatments of 6 and 22 beetles showed similar soil communities over time, indicating that dung beetle presence is more important than dung beetle abundance. Using the DESeq2 package in R, we found that bacteria and fungal families associated with nutrient cycling were overrepresented in treatments with both 6 and 22 dung beetles, as compared to treatments with no dung beetles.